JP2004206892A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug made of an electrode material with reduced consumption of the electrode and excellent durability. <P>SOLUTION: At least one of a center electrode and a ground electrode of the spark plug is made of an electrode material containing 0.5 to 1.5% of Si, 0.5 to 1.5% of Al, 0.05 to 0.5% of one or two components selected from the group consisting of Y, Nd and Sm, 0.8% or less of the total amount of Cr and Mn, and the rest consisting of Ni or inevitable impurities. The specific resistance of the electrode material at normal temperatures is adjusted to 25 μΩcm or less. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a spark plug.
[0002]
[Prior art]
BACKGROUND ART Conventionally, a spark plug used for ignition of an internal combustion engine such as an automobile engine generally includes a cylindrical metal shell, a cylindrical insulator disposed in an inner hole of the metal shell, and a tip side of the insulator. A center electrode disposed in the inner hole; and a ground electrode having one end fixed to the tip end of the metal shell and the other end forming a spark discharge gap with the center electrode.
[0003]
Conventionally, as an electrode material of a center electrode or a ground electrode of this type of spark plug, Ni is 0.5 to 1.5% (hereinafter,% means weight%) and Mn is 0.7 to 2.8%. A material made of a Ni-based alloy containing 0.25 to 4.5% of Al is known (see Patent Document 1). Ni containing 1.0 to 2.5% of Si, 0.5 to 2.5% of Cr, 0.5 to 2.0% of Mn, and 0.6 to 2.0% of Al A material for a spark plug made of a base alloy is also known (see Patent Document 2). These components are added in order to satisfy the performances of the spark plug, such as resistance to sulfur, lead corrosion, and high-temperature oxidation, and to suppress electrode consumption due to spark discharge and improve durability.
[0004]
[Patent Document 1]
JP-A-64-87738 [Patent Document 2]
JP-A-4-45239 [0005]
[Problems to be solved by the invention]
Recently, the demand for sulfur resistance and lead corrosion has been reduced compared to the past due to the improvement of fuel purification and combustion, but conversely, electrode wear due to spark discharge has been further suppressed and durability has been improved. The demands to do so are higher than ever. However, the spark plugs using the materials of Patent Documents 1 and 2 have not sufficiently satisfied the demand.
[0006]
An object of the present invention is to solve the above-mentioned problems of the related art, and to provide a spark plug made of an electrode material having reduced durability and reduced electrode wear.
[0007]
[Means for Solving the Problems and Their Functions and Effects]
Means for Solving the Problems The present invention has been made to solve the above-mentioned problems. The present invention provides a cylindrical metal shell, a cylindrical insulator arranged in an inner hole of the metal shell, and a center arranged in a tip side inner hole of the insulator. An electrode and a spark plug having one end fixed to the tip end side of the metal shell and the other end side forming a spark discharge gap with the center electrode, wherein at least one of the center electrode and the ground electrode has Si. 0.5 to 1.5% (% means weight%), Al is 0.5 to 1.5%, and one or two components selected from Y, Nd and Sm are 0.1%. Electrode material containing 0.5-0.5%, the total amount of Cr and Mn being 0.8% or less, the balance being Ni and unavoidable impurities, and the specific resistance at room temperature being adjusted to 25 μΩcm or less. It is characterized by comprising.
[0008]
(1) Outline of Material In order to respond to the above requirements, the inventors of the present invention have studied to suppress spark consumption of an electrode made of a Ni-based alloy. As a result, the specific resistance at room temperature is set to 25 μΩcm or less, thereby improving durability. It was found to improve. This is because, if the specific resistance of the electrode at room temperature exceeds 25 μΩcm, the temperature of the electrode rises during spark discharge, which accelerates the consumption of the electrode and impairs the durability. Therefore, the electrode material for a spark plug according to the present invention is a Ni-based alloy having a specific resistance of 25 μΩcm or less at normal temperature (20 ° C. to 25 ° C.), thereby improving durability and suppressing spark consumption of the electrode. can do.
[0009]
Further, in order to satisfy the minimum requirements of corrosion resistance and high-temperature oxidation resistance required for an electrode material composed of a Ni-based alloy, the additive components contained in Ni are adjusted. However, there is an additive component that increases the specific resistance at room temperature when the amount of the additive component increases. Therefore, the additive components are adjusted in order to make the electrode material satisfying the requirements of corrosion resistance and high-temperature oxidation resistance while keeping the specific resistance at room temperature to 25 μΩcm or less. In other words, the protective oxide film is formed by reducing the amount of Cr and Mn added, and adding Si and Al, and reinforcing the protective oxide film even with a small amount of Si and Al. , Nd, and Sm are added to the sample. Hereinafter, the operation of each component will be described.
[0010]
(2) Action of Cr and Mn Cr and Mn act to improve corrosion resistance and oxidation resistance by forming a protective oxide film on the surface of the spark plug. However, when the content increases, the specific resistance at room temperature increases. Therefore, the total amount of Cr and Mn is preferably 0.8% or less, particularly preferably 0.5% or less.
[0011]
(3) Function of Si Si has a function of improving corrosion resistance and high-temperature oxidation resistance by forming a protective oxide film on the surface layer of the spark plug electrode, and is added in an amount of 0.5 to 1.5%. If the addition amount is less than 0.5%, the effect is poor, while if it exceeds 1.5%, the specific resistance at normal temperature increases, and the effect of suppressing the consumption of the electrode cannot be obtained. The range of Si is preferably 0.5 to 1.0%.
[0012]
(4) Action of Al Al has a function of improving corrosion resistance and high-temperature oxidation resistance by forming a protective oxide film like Si, and is added in an amount of 0.5 to 1.5%. Similarly, when the addition amount of Al is less than 0.5%, the effect is poor. On the other hand, when the addition amount exceeds 1.5%, the specific resistance at room temperature increases, and the effect of suppressing the consumption of the electrode cannot be obtained. Preferably, it is 0.5 to 1.0%.
[0013]
(5) Action of Y, Nd, Sm Y, Nd, Sm strengthens the protective oxide film formed from Si and Al even if the total added amount of Cr or Mn is 0.8% or less. To improve corrosion resistance and high-temperature oxidation resistance. The protective oxide film of Al and Si is mainly composed of Al ₂ O ₃ on a matrix of a Ni-based alloy and SiO ₂ thereon, while a compound such as Y is composed of a matrix phase of Al ₂ O ₃ or SiO _2. To form a compound which exerts a wedge effect on the protective oxide film to enhance the adhesion between the protective oxide film and the matrix phase.
[0014]
In addition, the elements Y, Nd, and Sm have a strong affinity for O and S, and produce a compound with O and S that have penetrated into the inside of the electrode, and thus have an effect of delaying oxidation and sulfidation of the main component.
[0015]
Furthermore, since the addition amounts of Cr and Mn are set to 0.8% or less, crystal grains are likely to grow when the electrode is exposed to a high temperature, but this is suppressed by Y or the like. That is, since the internal oxidation of the electrode proceeds along the grain boundary, if the crystal grain boundary is reduced, the oxidation of the grain boundary easily proceeds to the center of the electrode, and there is a possibility that the internal oxidation leading to electrode damage may be caused. However, since Y, Nd, and Sm do not form a solid solution in Ni, they precipitate at the grain boundaries and perform a pinning effect, thereby preventing the crystal grains from becoming coarse.
[0016]
A preferable range for Y to obtain the above-mentioned effect is 0.05 to 0.5%. When the content is less than 0.05%, the effect is poor. On the other hand, when the content is more than 0.5%, plastic working for drawing a wire for a ground electrode and encapsulating a member having good thermal conductivity for a center electrode. This is because the property is reduced.
[0017]
(6) Action of C Further, in the present invention, 0.01 to 0.07% of C may be contained. C has the effect of increasing the mechanical strength at high temperatures. That is, in the above-mentioned Ni-based alloy, although the high-temperature strength is easily reduced, the deformation of the electrode due to thermal stress during use is hardly caused by the addition of C, which is an intrusive element. C is 0.01 to 0.07% in order to obtain such an effect. If C is less than 0.01, no effect can be obtained, and if C exceeds 0.07%, the deformation resistance of the spark plug electrode material becomes large, and a member having good thermal conductivity is used as the center electrode. This is because plastic working such as sealing becomes difficult.
[0018]
(8) Average Particle Size The crystal particles of the spark plug electrode material preferably have an average particle size of 300 μm or less after being kept at 900 ° C. for 100 hours. If it exceeds this, the electrode may be damaged due to grain boundary oxidation.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, production examples and test examples of the spark plug and the spark plug electrode material according to the present invention will be described. FIG. 1 is a cross-sectional view of a spark plug, FIG. 2 is a sample provided for an electrode material for a spark plug, and FIG. 3 is an explanatory diagram illustrating the results of an evaluation test of each sample.
[0020]
A spark plug 100 as an example of the present invention shown in FIG. 1 has a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that the tip side protrudes, and an insulator 2 so that the tip side protrudes. One end is connected to the center electrode 3 provided inside the metal member 1 and the metal shell 1 by welding or the like, and the other end is bent back to the center electrode side, and is disposed so as to face the front end of the center electrode 3. A ground electrode 4 and the like are provided. The gap between the center electrode 3 and the opposing ground electrode 4 is a spark discharge gap g.
[0021]
The metal shell 1 is made of low carbon steel or the like, and has a substantially cylindrical shape. The metal shell has a flange portion 11 protruding in the radial direction and a tool having a hexagonal cross section which is located on the proximal side thereof and which is engaged with a tool such as a spanner when the spark plug 100 is attached to a cylinder head or the like of an engine. It has an engagement portion 12 and a tip portion 13 located on the tip side from the flange portion and having a smaller diameter than the flange portion. A screw 14 for screwing the spark plug 100 to a cylinder head or the like of the engine is formed on the outer periphery of the distal end 13. A crimping portion 15 for crimping and fixing the insulator 2 to the metal shell 1 is provided on the base end side of the tool engaging portion 12.
[0022]
On the other hand, the insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has an axial hole 2H for fitting the center electrode 3 along its own axial direction. Of the shaft hole 2H, the center electrode 3 is fixed to the distal end, and the terminal fitting 5 is fixed to the proximal end. In this shaft hole 2H, a resistor 6 is arranged between the center electrode 3 and the terminal fitting 5. Both ends of the resistor 6 are electrically connected to the center electrode 3 and the terminal fitting 5 by a conductive glass seal 7.
[0023]
The insulator 2 has a protruding portion 21 that protrudes in the radial direction, and a base end portion 22 smaller in diameter than the protruding portion formed on the base end side. On the other hand, an intermediate body 23 having a diameter smaller than that of the protruding portion 21 is formed on the distal end side of the protruding portion 21, and a leg portion 24 is further formed on the distal end side.
[0024]
The center electrode 3 has a good heat conductive core 31 made of copper or the like, and a coating 32 made of the above-described material, and the tip of the coating 32 is arranged so as to protrude from the tip of the insulator 2 toward the tip. ing. On the other hand, one end of the ground electrode 4 is fixed to the distal end surface of the metal shell 1, and the other end is bent back toward the center electrode side, and is arranged so as to face the distal end of the center electrode 3.
[0025]
【Example】
Next, in order to confirm the effect of the present invention, the following experiment was performed.
Each sample of FIG. 2 was used and manufactured by the following steps. That is, a molten metal of an alloy having each component composition was prepared using a normal vacuum melting furnace, and was made into an ingot by vacuum casting. Thereafter, the ingot was formed into a round bar having a diameter of 60 mm by hot forging. This round bar was subjected to wire drawing to obtain a wire having a diameter of 4 mm and a wire having a cross-sectional dimension of 1.6 mm × 2.8 mm. The former was formed as the center electrode 3 of the spark plug, and the latter was formed as the ground electrode 4. Then, the center electrode 3 is assembled to the shaft hole 2H of the insulator 2, the resistor 7 and the terminal fitting 6 are assembled by a known method, and glass sealing is performed. Then, the insulator 2 is assembled to the metal shell 1, one end of the ground electrode 4 is fixed to the metal shell 1, and the other end is folded back toward the center electrode so as to face the tip of the center electrode.
[0026]
In FIG. 2, in Examples 1 to 5, Si is 0.5 to 1.5%, Al is 0.5 to 1.5%, and one or two types are selected from Y, Nd and Sm. Component has a content of 0.05 to 0.5%, the total amount of Cr and Mn is 0.8% or less, and the balance consists of Ni and unavoidable impurities, and the specific resistance at room temperature is 25 μΩcm or less. Has been prepared.
[0027]
In Examples 6 to 8, the content of C or the average particle size of the crystals was adjusted to the range of Example 1 and the like, and corresponds to the scope of claim 2 or claim 3. That is, in Example 6, C is 0.003%, which is smaller than 0.01% (the lower limit of claim 2). In Example 7, C is 0.10%, which is more than 0.07% (the upper limit of claim 2). In Example 8, the average grain size of the crystals was 400 μm, which exceeded the upper limit of 300 μm described above.
[0028]
Comparative Examples 1 to 9 were created to examine the upper and lower limits of the above example. That is, in Comparative Example 1, the content of Si is 2.0% and exceeds the upper limit of 1.5% of Si. In Comparative Example 2, Al does not satisfy the lower limit of 0.5%, that is, does not contain Al. In Comparative Example 3, Nd is 0.02%, which is smaller than the lower limit of 0.05% described above. In Comparative Example 4, Y + Nd is 0.6%, which is larger than the above-mentioned upper limit value of 0.5%. In Comparative Example 5, the room temperature resistivity is 28 μm, which is larger than the above-mentioned upper limit of 25 μm. In Comparative Example 6, the content of Si is 0.2%, which is smaller than the above-described lower limit of 0.5%. In Comparative Example 7, Al is 2.0% which is larger than the above-mentioned upper limit of 1.5%. In Comparative Example 8, the total weight of Cr and Mn is 1.2%, which is larger than the upper limit of 0.8%. Comparative Example 9 corresponds to the conventional technique.
[0029]
This test was performed on each sample by measuring the increase in the gap before and after the durability test by engine simulation. The engine used in the evaluation was a 6-cylinder, 2.8-liter engine. A durability test was performed at 160 km / h for about 400 hours, and the amount of increase in the cap before and after the durability test was measured.
As evaluation criteria, less than 0.3 mm was judged as good, 0.30 mm or more and less than 0.35 mm was judged as acceptable, and 0.35 mm or more was judged as unacceptable.
[0030]
This test was performed for each sample by measuring the oxide film thickness after the test by an engine simulation test. The engine used in the evaluation was a 4-cylinder, 2.0-liter engine. The period of rotating the engine at 5000 rpm and the period of idling were repeated at one minute intervals for 100 hours. The maximum temperature at this time was 900 ° C. The oxide film thickness formed on the ground electrode surface after the test was measured. In the case where grain boundary oxidation is observed in the oxide film, the film thickness is set to include the grain boundary oxidation.
As evaluation criteria, less than 180 μm was judged as good, 180 μm or more and less than 210 μm was judged as acceptable, and 210 μm or more was judged as unacceptable. This is because if the oxide film becomes too thick, the temperature of the electrode itself rises too much, so that the protective oxide film is desirably thin.
[0031]
This test was performed by measuring the amount of deformation of the center electrode by subjecting the center electrode to a thermal cycle. That is, the tip of the center electrode was heated to 850 ° C. for 3 minutes and air-cooled for 1 minute, and this was repeated as one cycle. And it evaluated by the number of cycles until the length of the center electrode was shortened by 0.1 mm.
The evaluation criteria were determined to be good for 2500 cycles or more and acceptable for less than 2500 cycles.
[0032]
The plastic workability was determined based on the workability of enclosing a member having good thermal conductivity in the center electrode.
[0033]
In all of Examples 1 to 5, good evaluations could be obtained. In Example 6, since the content of C was as small as 0.003%, evaluation by the center electrode deformation test was possible. In Example 7, since the content of C was as large as 0.1%, plastic workability was slightly inferior and acceptable. In Example 8, since the average crystal grain size was as large as 400 μm, evaluation by an oxide film thickness test was possible.
Thus, it can be seen that those having a gap test, an oxide film thickness test, a center electrode deformation test, and a plastic workability that are all acceptable can be used with excellent durability as an electrode material for a spark plug. If higher durability is required, it is preferable to select a material that will be good for all tests.
[0034]
In Comparative Example 1, since the Si content was as large as 2%, the specific resistance was as large as 30 μΩm, and the increase in the electrode gap was as large as 0.36 mm, which was not possible. In Comparative Example 2, since Al was not included, the thickness of the oxide film was as thick as 250 mm, which was unacceptable. In Comparative Example 3, since Nd was as small as 0.02%, the oxide film thickness was 250 mm or more, which was not possible. In Comparative Example 4, since Y + Nd was as large as 0.6%, plastic workability was not possible. In Comparative Example 5, since the specific resistance was as large as 28 μΩm, it was as large as 0.35 mm, which was not possible. In Comparative Example 6, since the content of Si was as small as 0.2%, a thick oxide film having a thickness of 220 μm was impossible. In Comparative Example 7, since the Al content was as high as 2.0%, the increase in the electrode gap was as large as 0.36 mm, which was not possible. In Comparative Example 8, since the total amount of Cr and Mn was as large as 1.2%, the increase in the electrode gap was as large as 0.36 mm, which was impossible. Comparative Example 9 corresponds to the conventional technique, and has a large specific resistance at room temperature. Therefore, the increase in the electrode gap is as large as 0.40 mm, which is not possible.
[0035]
The present invention is not limited to the above embodiment, but can be implemented in various modes without departing from the scope of the invention. In the spark plug of the present invention, the screw portion 5 is formed. However, the present invention is not limited to this, and a spark plug having no screw portion may be used.
Further, in the embodiment, the ground electrode 4 is formed of the material composed only of the material of the present invention. However, the present invention is not limited to this. It may be a ground electrode made of a coating layer made of a material. Further, in the embodiment, the center electrode 3 is formed of the good heat conductive core 31 made of copper or the like and the covering portion 32 made of the above-described material. However, the present invention is not limited to this. It may be formed more.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a spark plug of the present invention in which an electrode material is used.
FIG. 2 is an explanatory diagram illustrating a sample provided for an electrode material for a spark plug.
FIG. 3 is an explanatory diagram illustrating results of an evaluation test of each sample.
[Explanation of symbols]
100 spark plug 1 metal shell 2 insulator 3 center electrode 4 ground electrode 5 terminal metal 6 resistor 7 glass seal

Claims (3)

A cylindrical metal shell, a cylindrical insulator disposed in an inner hole of the metal shell, a center electrode disposed in a distal inner hole of the insulator, and one end fixed to the distal end of the metal shell. In the spark plug, the other end side has a ground electrode forming a spark discharge gap with the center electrode,
At least one of the center electrode and the ground electrode contains 0.5 to 1.5% of Si (hereinafter,% means weight%), 0.5 to 1.5% of Al, Y, Nd or Sm. One or two components selected from them contain 0.05 to 0.5%,
It is characterized in that the total amount of Cr and Mn is 0.8% or less, the balance is made of Ni and unavoidable impurities, and the electrode material is adjusted to have a specific resistance at room temperature of 25 μΩcm or less. Spark plug. The spark plug according to claim 1,
A spark plug, wherein the electrode material contains 0.01 to 0.07% of C. In the spark plug according to claim 1 or 2,
A spark plug in which the electrode material has an average crystal grain size of 300 μm or less after holding at 900 ° C. for 100 hours.

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